This invention relates to a method of retreading tires, and more particularly to a tire retreading curing ring apparatus.
In general, there are two methods of retreading a worn-out tire to make it suitable for continued use. The methods include retreading a tire in a standard retread mold or, alternatively, utilizing moldless retreading. For example, tires to be retreaded in molds are buffed and then covered with a layer of uncured rubber, and placed in a standard tire retread mold. The rubber is shaped to the desired tread pattern by applying pressure inside the tire and then heating the entire assembly until the uncured rubber is cured and bonded to the carcass.
In moldless retreading, on the other hand, the tire assembly is formed on a tire carcass. A tread strip is placed on the peripheral or circumferential surface of the carcass, and a binder material or gum is placed between the surface and the tread strip. The assembly is then placed in a flexible envelope and the prevulcanized tread strip is vulcanized onto the tire carcass. Normally, the tire is mounted on a rim prior to enclosing the assembly within the flexible envelope. This invention, however, is directed to a tire retread curing ring apparatus which avoids the need for mounting the tire carcass on a rim or the necessity for using an inner tube to shape the tire in an envelope-type of retreading process.
More specifically, heretofore, various apparatus have been devised to accomplish sealing the envelope which covers the entire tire assembly and the tire bead. In particular, U.S. Pat. No. 4,579,619 discloses the use of a rigid circular ring sized to fit adjacent the bead area of the tire. Mounted on the circular ring is a plurality of clamps having a pivoted arm positioned to engage the inner side of the bead of the tire. The clamps have a handle to move the pivot arm and force it against the tire bead, thereby drawing the ring against the envelope on the outer side of the bead. Once the tire assembly has been prepared for recapping, the circular rings are placed in position on the tire assembly and the clamps are operated to the closed position for sealing engagement. The tire assembly, with the ring apparatus attached, is placed in a chamber to complete the recapping process under increased temperatures and pressures. One of the deficiencies of this apparatus, however, is that the mechanical clamps do not always provide pressure sufficient to seal the envelope of the tire assembly against the side walls or beads of the tire to prevent gas leakage during recapping.
In accordance with this invention, a specially designed elastomeric gasket is positioned between the tire bead and the ring assembly which, together with positioning of the clamps, vastly improves the seal at the point of contact and avoids any leakage during the recapping process. To obtain maximum sealing, the clamps should be in a position such that the vertical axis of the clamp rod is aligned with the vertical axis of the clamp arm and a gasket. Preferably. the gasket has a hollow portion which makes it more resilient in order to more evenly distribute forces and seal the circular rings, the envelope, and the tire bead. Circumferential ribs on the gasket further enable the clamp arm to be pivoted against the tire bead and the gasket to form a tight seal, and thereby prevent any leakage of gas or air during the recapping process.